Soil Carbon Sequestration Potential of Climate-Smart Villages in East African Countries

Assessing soil system changes under climate-smart agriculture via farmers' observations and conventional soil testing

Soil degradation remains a challenge in African highlands, where land management lacks a strong context-specific evidence base. We investigated the impacts of recently implemented soil and water conservation (SWC) practices-farmyard manure addition, incorporation of crop residues in soil and fanya juu terracing under an agroforestry system on soil health indicators in the East Usambara Mountains of Tanzania. Farmers' observations of soil changes were combined with conventional soil testing to assess the initial impacts of SWC practices relative to conventional non-SWC practice. Majority of farmers (66%-83%) reported that combining fanya juu terracing with organic amendments led to soil colour change from red to black and an increase in crop yield. Despite the observed darkening of the soil, there was no significant increase in soil organic carbon stock and the contents of N, P, K. There were important changes in soil physical properties, including greater aggregate stability (mean weight diameter of 1.51-1.71 mm) in the SWC plots, a greater volume of transmission pores (>60 μm) and coarse storage pores (10-60 μm) in the surface soil layer (0-15 cm), and greater volume of fine storage pores (0.2-10 μm) and residual pores (0.2 μm) in the sub-surface layer (15-30 cm) of the SWC plots compared with the conventional plots. These changes indicate that SWC rapidly enhances infiltration and retention of water within the root zone, which are important for increasing crop yields and improving the resilience of the agro-ecosystem to environmental stress. Combining SWC with effective soil fertility management is needed for sustainable highland agriculture.

Responses of soil organic carbon to conservation practices including climate-smart agriculture in tropical and subtropical regions: A meta-analysis

Considering the current threatening conditions of climate change, Climate Smart Agriculture (CSA) aims to improve the soil health and its organic carbon stocks by encouraging soil carbon sequestration through conservation practices in agricultural lands. However, the effects of these practices differ due to diverse climatic scenario, soil characteristics and management system. To identify the suitable practices that can be effective under tropical and subtropical conditions, a systematic evaluation in the form of a meta-analysis of these practices and their outcomes was performed over those regions. In this work we have included 516 observations from 84 articles published from 2000 to 2021 to analyse the influence of three CSA practices (conservation tillage, cover crop and biochar application) on the SOC (soil organic carbon) stocks over varying periods of experimentation. In addition to this, the combined effect of CSA and other conservation agronomic practices such as agroforestry has also been considered in the analysis. The results showed that biochar application had the most influence upon SOC stocks in the agricultural lands (25.38%) followed by conservation tillage (18.81%) and cover crop (15.8%). Medium term experiments (6-20 years) of these conservation practices showed about 31.00-96.15%improvement in SOC while the effects gradually diminished in long term experiments (>20 years). The combinations of these practices have been observed to have an evidently positive impact upon the SOC stocks in general. This work provides a systematic evaluation of all the widely performed CSA and other conservation practices and their effects on SOC dynamics under differing management settings.

Ensemble Modeling on Near-Infrared Spectra as Rapid Tool for Assessment of Soil Health Indicators for Sustainable Food Production Systems

A novel total ensemble (TE) algorithm was developed and compared with random forest optimization (RFO), gradient boosted machines (GBM), partial least squares (PLS), Cubist and Bayesian additive regression tree (BART) algorithms to predict numerous soil health indicators in soils with diverse climate-smart land uses at different soil depths. The study investigated how land-use practices affect several soil health indicators. Good predictions using the ensemble method were obtained for total carbon (R2 = 0.87; RMSE = 0.39; RPIQ = 1.36 and RPD = 1.51), total nitrogen (R2 = 0.82; RMSE = 0.03; RPIQ = 2.00 and RPD = 1.60), and exchangeable bases, m3. Cu, m3. Fe, m3. B, m3. Mn, exchangeable Na, Ca (R2 > 0.70). The performances of algorithms were in order of TE > Cubist > BART > PLS > GBM > RFO. Soil properties differed significantly among land uses and between soil depths. In Kenya, however, soil pH was not significant, except at depths of 45–100 cm, while the Fe levels in Tanzanian grassland were significantly high at all depths. Ugandan agroforestry had a substantially high concentration of ExCa at 0–15 cm. The total ensemble method showed better predictions as compared to other algorithms. Climate-smart land-use practices to preserve soil quality can be adopted for sustainable food production systems.

The Effect of Climate-Smart Agriculture on Soil Fertility, Crop Yield, and Soil Carbon in Southern Ethiopia

It is critical to develop technologies that simultaneously improve agricultural production, offset impacts of climate change, and ensure food security in a changing climate. Within this context, considerable attention has been given to climate-smart agricultural practices (CSA). This study was conducted to investigate the effects of integrating different CSA practices on crop production, soil fertility, and carbon sequestration after being practiced continuously for up to 10 years. The CSA practices include use of soil and water conservation (SWC) structures combined with biological measures, hedgerow planting, crop residue management, grazing management, crop rotation, and perennial crop-based agroforestry systems. The landscapes with CSA interventions were compared to farmers’ business-as-usual practices (i.e., control). Wheat (Triticum sp.) yield was quantified from 245 households. The results demonstrated that yield was 30–45% higher under CSA practices than the control (p < 0.05). The total carbon stored at a soil depth of 1 m was three- to seven-fold higher under CSA landscapes than the control. CSA interventions slightly increased the soil pH and exhibited 2.2–2.6 and 1.7–2.7 times more total nitrogen and plant-available phosphorus content, respectively, than the control. The time series Normalized Difference Water Index (NDWI) revealed higher soil moisture content under CSA. The findings illustrated the substantial opportunity of integrating CSA practices to build climate change resilience of resource-poor farmers through improving crop yield, reducing nutrient depletion, and mitigating GHG emissions through soil carbon sequestration.